Free standing quantum dots (FSQDs) are semiconductor nanocrystallites whose radii are smaller than the bulk exciton Bohr radius and constitute a class of materials intermediate between molecular and bulk forms of matter. FSQDs are known for the unique properties that they possess as a result of both their small size and their high surface area. For example, FSQDs typically have larger absorption cross-sections than comparable organic dyes, higher quantum yields, better chemical and photo-chemical stability, narrower and more symmetric emission spectra, and a larger Stokes shift. Furthermore, the absorption and emission properties vary with the particle size and can be systematically tailored. It has been found that a Cadmium Selenium (CdSe) quantum dot, for example, can emit light in any monochromatic, visible color, where the particular color characteristic of that dot is dependent on the size of the quantum dot.
FSQDs are easily incorporated into or on other materials such as polymers and polymer composites because FSQDs are highly soluble and have little degradation over time. These properties allow FSQD polymers and polymer composites to provide very bright displays, returning almost 100% quantum yield.
Applications for FSQD polymers and polymer composites include point of purchase and point of sale posters, mobile device housings or logos, segmented displays, including ultraviolet (UV) and infrared (IR) displays, absorbers for UV and IR sensors or detectors, and light emitting diodes (LEDs). Although the visible advantages inherent to FSQD polymers and polymer composites are attractive, control of the output (light intensity) is problematic.
Accordingly, it is desirable to provide an apparatus and method of modulating the photon output of a FSQD light emitting device. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.